1. Field of the Invention
The present invention relates to an improved igniter for solid fuel rocket motors and has particular utility in high performance full, head-end web solid propellant rocket motors.
2. Description of the Prior Art
The conventional igniter for large solid fuel rocket motors is a miniature rocket motor that is known in the art as a "pyrogen" igniter. Typically, a pyrogen igniter is mounted in the forward end of a motor through a hole in the propellant. In some high-performance rocket motors, however, a pyrogen igniter is impractical to use because of the full, head-end web of the propellant in the forward end of the motor. The head-end web propellant grain design has the primary advantage providing a higher mass fraction.
Full, head-end web solid propellant rocket motors are now being developed which have the capability of being offloaded, that is, having some of the propellant grain removed, to meet the specific total impulse requirements. This offload is achieved by machining out propellant from the aft end of the motor. As propellant is removed, the internal free volume of the motor increases proportionately. The larger free volume makes ignition of the motor more difficult. One way to improve the ignition process is to mount the igniter to the aft end of the motor propellant grain. The source of heat for ignition thus remains as close as possible to the surface being ignited, regardless of the degree of offload.
Mounting the igniter to the motor propellant grain introduces a problem. This is because upon ignition and burning of the propellant grain at the aft end of the motor the support for the igniter erodes. Such erosion tends to cause the igniter to become detached from the propellant grain with possible resulting damage to the rocket motor nozzle or the propellant. In order to avoid such damage, the igniter must be substantially consumed before becoming detached from the propellant. Additionally, the igniter must perform its intended function of igniting the propellant grain before being consumed. A further requirement is that the igniter must exhaust its output across the surface of the motor propellant surface regardless of the percent of offload.